1. Field of the Invention
The present invention relates to a semiconductor device including a memory circuit.
2. Description of the Related Art
Now products with CPUs, e.g. appliances and computers, have spread in the world and serve as necessities in our life. Generally, these products are equipped with integrated circuit components such as a dedicated circuit having a specific function, a memory, and the like. For example, in a product with a CPU and a memory, the memory functions as a program storage area or working area of the CPU.
As a product with a CPU and a memory, for example, a semiconductor device capable of radio communication as disclosed in Reference 1 (Hiroki Dembo et al, “RFCPUs on Glass and Plastic Substrates Fabricated by TFT Transfer Technology”, IEEE, TECHNICAL DIGEST OF INTERNATIONAL ELECTRON DEVICES MEETING, Dec. 5, 2005, pp. 1067-1069) is well known. Such a semiconductor device is called a wireless chip, wireless IC, or the like.
For improvement in performance of a product with a CPU, the CPU is required to improve in operation speed. Furthermore, for improvement in operation speed of the CPU, a memory is required to operate at higher speed. As a result, power consumption of the memory accounts for the major part of that of a circuit portion. However, the fact is that there is no attempt to reduce power consumption in the aspect of the whole system integrated with the CPU and memory although the power consumption of individual components is attempted to be cut down, for in general the CPU and the memory are designed separately as versatile components.